OEIGIN OF THE SOIL 19 



long distances, dragging them over the bed rock, grinding 

 them against other pieces, and rapidly reducing them in size, 

 the finer particles being carried away by the current and 

 deposited elsewhere. Waterworn pebbles are easily recog- 

 nized by their rounded surfaces, and the fine sand and clay 



Photozraph by II. L. Ilollister Land Co. 



FIG. 7. A mountainous region showing the weathered crests and 

 snow-filled valleys 



to be found in every shallow are but deposits of rock dust 

 ground from the pebbles by the streams. 



It is not alone the particles of rock in the stream beds 

 that are carried away by running water. During every heavy 

 rain the torrents of muddy water running away from culti- 

 vated fields show how rapidly the most fertile parts are be- 

 ing removed. When the current slackens, this material is 

 dropped, the largest particles first, the smallest much later. 

 The latter often continue suspended in the water for days. 



